This invention relates to a method for determining the condition of the effectiveness of shock absorption of a spring running gear, particularly undercarriage of a road motor vehicle with elastic tires and to an apparatus for carrying the method into practice.
The importance of testing of shock absorbers while installed in a vehicle running gear (suspension) system from the point of traffic safety is presently known. For solving of said task several solutions are developed, which all have a common feature that they are based on measurement of the number of oscillations of the car body or the damping of the wheel oscillation. Accordingly, an oscillation of the car body or the wheels is generated and the displacements meanwhile are registered. The magnitude of the oscillations of the car body has an influence on the comfort of the passengers, the evaluation of this magnitude yields no satisfying result according to the observations for the condition of effectiveness of shock absorbers in the vehicle with a view of traffic safety.
An apparatus for testing of built-in shock absorbers is known as well, in which a drive motor swings a support plate through an eccentric and a spring and the wheels of the running gear to be tested are placed on the support plate. During testing the energizing frequency is increased a little bit over the natural frequency of the running gear, then the energizing frequency is slowly decreased by switching off the power. The energizing frequency passes through the natural frequency of the running gear in this retardation cycle and the displacements of the support plate are registered during the running out. (Such a test apparatus is, for example of the German company "BOGE", well known.)
The shortcomings of the above mentioned solution lie in that the condition of the tested system does not meet the requirements of the real traffic conditions because the natural frequency of the apparatus depends on the rigidity of the springs of the test stand, the mass of the support plate, the unsprung mass of the running gear (undercarriage) and the spring of the car body, as well. Thereupon, the oscillating system will be mistuned and the measured value of the resonant amplitude and the behavior of the shock absorbers with a view of traffic safety can be made only by correlation with much circumstance. A necessary conditon of it is the full knowledge of the limiting values which depend on the production of the shock absorbers and vehicles. This makes the operation of the apparatus extremely difficult in case of heterogeneous vehicle fleets and set for the operator a tedious task.
For approximation of the real traffic conditions and for general purpose of the qualification the Hungarian patent specification No. 176.823 describes a solution comprising the steps of sensing the changes of the wheel load during the speed-up and slowing down cycles produced by the energizing frequency, determining the average wheel load by electrical process, comparing the minimum wheel load occurring at the natural frequency of the running gear in the slowing down cycle to the average value of the wheel load and qualifying the shock absorbers. The apparatus for performing said method is provided with a support plate and co-operating energizing means connected to said support plate through a double-arm lever, wherein the fulcrum of the lever is joined with a force sensing unit. The force sensing unit is connected to an electronical measuring unit.
In the above solution a ratio is formed by division of the average wheel load by the minimum wheel load occurring at the natural frequency of the running gear and the quality of the shock absorber is displayed in percentage, but a major share of the full quality range remains unused. An oscillation of the wheel load in some degree is always generated by the energizing amplitude and the rubber rigidity, so that a seventy-five-eighty percent quality results in the case of the theoretically attainable upper limit.